Britain could lose its continuous nuclear deterrence programme under a scenario that has been outlined in a government-commissioned report examining alternatives to Trident.

The report, to be published on Tuesday, is expected to discuss a range of alternatives to the current system under which a submarine armed with nuclear warheads is at sea and ready to be deployed at all times. It provides explicit detail on the costs associated with Britain's commitment to nuclear weapons and is expected to be the subject of a parliamentary debate on Wednesday.

Although it does not make any recommendations, the scenarios it outlines are likely to ignite a political row. The Conservatives are fully committed to Trident but the Liberal Democrats are opposed. Labour has pledged to study the contents of the report before outlining its position.However, while the Tories will seek to dismiss its importance, the report will help frame the debate about Britain's long-term nuclear weapons capabilities in the runup to the general election. It is likely that Trident would become a political bargaining chip in any power-sharing deal between Labour and the Lib Dems.

Any diminution of Britain's capabilities would be a major shift in policy that has been entrenched since the cold war. The current nuclear deterrence system involves four submarines on permanent rotation with one at sea at all times. Four is considered the minimum number of submarines needed to maintain a continuous presence at sea. But the report has examined alternative options, including the use of ships or planes. However, none of these options, known as "postures" in military circles, is considered viable. There is also the added complication that the government has already made financial commitments to develop the next generation of nuclear submarines. Instead the report will suggest one potential posture could be to reduce the number of submarines from four to two or three. This would mean an end to continuous at-sea nuclear deterrence.

Anti-nuclear campaigners would welcome any move to cut the UK's nuclear weapons programme. "It seems highly likely that the report will highlight that there are alternatives to 'like-for-like' replacement of Trident and that the UK's security does not require keeping a nuclear-armed submarine at sea at all times," said Peter Burt of the Nuclear Information Service. "By taking Trident off permanent patrol, the UK now has an opportunity to make a decisive move which would dramatically boost our international status as a global leader and, as the US's closest ally, signal our firm support for President Obama's international arms control agenda."

Nick Harvey, the Lib Dem MP and former defence minister who initiated the report, said it would send clear signals to the rest of the world if the UK scaled back its nuclear weapons capabilities. "If the UK, as one of the five original nuclear powers, were to do this, it would give fresh encouragement to non-proliferation," Harvey said.

An increasing number of high-profile politicians have questioned the UK's commitment to Trident. Labour's former defence secretary, Des Browne, has argued that the world has changed since the cold war. Experts point out that the UK stopped targeting its nuclear missiles at Russia in 1994.

But any scaling back of Trident would carry geopolitical consequences. "The issue now for politicians is not whether the UK should take the Trident submarines off permanent nuclear patrol," Burt said, "but how to do it in a way which maximises diplomatic clout and leads to other nuclear-armed states taking similar steps.